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Animal Cells Animals Cadherins & Cell Junctions Extracellular Matrix Animal Tissues & Development Animal Development & Differentiation Tissues and Morphogenesis Animal Cells • Eukaryotic • No cell wall No plastids No central vacuole • Multicellular: – extensive specialization & differentiation – unique cell-cell junctions Fig. 6.8 Animals Cadherins & Cell junctions • Motile Cadherins • Highly differentiated • “calcium-dependent adhesion” transmembrane proteins tissues – Tissue-specific • Intercellular junctions • Δ [Ca++] Þ Δ adhesion strength – Allow developmental – tissue-specific cadherins cell migration • Δ cadherin type Þ Δ binding • Extracellular protein – Allow developmental fibers tissue separation – collagen • Diploid life cycle • Blastula/gastrula embryo Extracellular Matrix (ECM) post-fertilization events 1 Binding of sperm to egg • Collagen fibers • sea urchin 2 Acrosomal reaction: plasma membrane (echinoderm), a 3 depolarization (fast block to polyspermy) • Elastin fibers 4 model organism • Fibronectin 6 8 – Attachment / movement along ECM 10 Seconds Increased intracellular calcium level 20 Cortical reaction begins (slow block to polyspermy) Sperm 30 head 40 50 1 Formation of fertilization envelope complete EGG CYTOPLASM 2 Increased intracellular pH 3 4 5 Increased protein synthesis 10 Minutes 20 Fusion of egg and sperm nuclei complete 30 40 Onset of DNA synthesis 60 90 First cell division Figure 47.5 Heyer 1 Animal Tissues & Development Cleavage: DNA replication / mitosis / cytokinesis with no growth phases products of cytokinesis smaller & smaller blastomeres Spiral vs. Radial Cleavage • Protostomes: “mouth first” – most invertebrates S S – spiral cleavage G1 G2 M – determinate M • Deuterostomes: “mouth second” Cell cycle during Cell cycle after – echinoderms cleavage stage cleavage stage & vertebrates – radial cleavage – indeterminate • Little/no synthesis of new RNA or proteins • All cells dependent upon molecular machines from original ovum Determinate cleavage in a protostome (round worm) DeterminAte cleAvAge in A protostome (round worm) 0 Zygote Cytoplasmic determinates – RNA-protein complexes First cell division •Define cell fate and body axis. Nervous Musculature, Outer skin, Germ line • E.g., “P-granules” in round worm embryo system, gonads nervous system (future outer skin, gametes) • Dispersed in egg cell muscula- ture Musculature • After fertilization, aggregates at future posterior end 20 μm • Upon each cleavage, partition to posterior-most cell Time after fertilization (hours) 10 Hatching Intestine Intestine 1 Newly fertilized egg 3 Two-cell embryo Mouth Anus Eggs Vulva ANTERIOR POSTERIOR 1.2 mm 2 Zygote prior to first division 4 Four-cell embryo Figure 47.19 Caenorhabditis elegans Figure 47.21 Indeterminate cleavage in a deuterostome (frog) Experiment Blastulation — Sea Urchin Control egg Experimental egg (dorsal view) (side view) • Cleavage partitions the cytoplasm of one large cell into 1a 1b Gray many smaller cells called blastomeres Gray crescent crescent • Continued cleavage è hollow structure called a blastula – The hollow cavity is the blastocoel Thread • In general, tissue-specific fates of cells are fixed by the late gastrula stage 2 Results (a) Fertilized egg. Shown (b) Four-cell stage. (c) Morula. After further (d) Blastula. A single layer of here is the zygote shortly Remnants of the cleavage divisions, the cells surrounds a large before the first cleavage mitotic spindle can be embryo is a multicellular blastocoel cavity. division, surrounded by seen between the two ball that is still surrounded Although not visible here, the fertilization envelope. cells that have just by the fertilization the fertilization envelope The nucleus is visible in completed the second envelope. The blastocoel is still present; the embryo the center. cleavage division. cavity has begun to form. will soon hatch from it and Normal Belly piece Normal begin swimming. Figure 47.23 Figure 47.6 Heyer 2 Animal Tissues & Development Animal Morphogenesis Morphogenesis • Creation of form - directed by genes • In plants, by differential growth – Cell proliferation • In animals, by both growth & cell migration – Cell migration – Cell differentiation Cell Gut movement – Cell death (apoptosis) Zygote Eight cells Blastula Gastrula Adult animal (fertilized egg) (cross section) (cross section) (sea star) Cell division Morphogenesis Observable cell differentiation Seed leaves Shoot apical meristem Root apical Zygote meristem Figure 21.4 (fertilized egg) Two cells Embryo inside seed Plant Blastulation & Gastrulation Primary embryonic germ layers • Early embryonic development in animals • Diploblastic: two germ layers 3 In most animals, cleavage results in the – Ectoderm: develops into epidermal & neural tissues 1 The zygote of an animal formation of a multicellular stage called a blastula. The blastula of many animals is a undergoes a succession of mitotic – Endoderm: develops into feeding tissues cell divisions called cleavage. hollow ball of cells. – Blastocoel: becomes filled with acellular mesoglia Blastocoel Cleavage Cleavage Blastocoel 6 The endoderm of the archenteron Examples: develops into Eight-cell stage Blastula Cross section Zygote Endoderm the the animal’s of blastula Porifera & Cnidaria digestive tract. Blastocoel Endoderm 5 The blind Ectoderm pouch formed by Ectoderm gastrulation, called the archenteron, opens to the outside Gastrula Gastrulation via the blastopore. Blastopore 4 Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the Blastopore blastocoel, producing layers of embryonic tissues: the Figure 32.2 ectoderm (outer layer) and the endoderm (inner layer). Primary embryonic germ layers • Triploblastic: three germ layers Triploblastic gastrulation forms – Ectoderm: develops into epidermal & neural tissues three germ layers – Endoderm: develops into gut & accessory organs ECTODERM MESODERM ENDODERM – Mesoderm — displaces blastocoel: develops into • Epidermis of skin and its • Notochord • Epithelial lining of muscle, connective tissues, & vasculature derivatives (including sweat • Endoskeletal system digestive tract glands, hair follicles) • Muscular system • Epithelial lining of • Epithelial lining of mouth • Muscular layer of respiratory system and rectum stomach, intestine, etc. • Lining of urethra, urinary Examples: • Sense receptors in • Excretory system bladder, and reproductive everything else epidermis • Circulatory and lymphatic system • Cornea and lens of eye systems • Liver • Nervous system • Reproductive system • Pancreas Archenteron • Adrenal medulla (except germ cells) • Thymus • Tooth enamel • Dermis of skin • Thyroid and parathyroid • Epithelium or pineal and • Lining of body cavity glands pituitary glands • Adrenal cortex Figure 47.16 Mesoderm Blastopore Figure 32.10b Heyer 3 Animal Tissues & Development c.f., Figure 40.5 Epithelial Tissue Triploblastic Animal Tissues • Typical mammalian body is composed of ~50,000,000,000,000 cells • Continuous sheet • Typical vertebrate body is composed of >100 or layers of cells specialized types of cells (tissue types) with direct cell- – Grouped into four major tissue types: cell junctions • Epithelial • All three germ • Connective layers start as epithelia, so • Muscle epithelial tissues • Nervous may derive from any germ layer. c.f., Figure 40.5 Connective Tissue Connective Tissue • Cells are • Cells are suspended in an suspended in an extracellular extracellular matrix. Epithelial tissue matrix. – often largely (Mucosa) – often largely composed of composed of collagen collagen fibers. Connective Mesenchyme fibers. tissue cells • Derived from • Derived from mesoderm. mesoderm. c.f., Figure 40.5 c.f., Figure 40.5 Muscle Tissue Nervous Tissue • Specialized to conduct electrochemical • Specialized for nerve impulses. contraction. • Derived from Note: “Nerve” = • Derived from ectoderm. bundle of axons from mesoderm. multiple neurons Glia 15 • Diploblastic Neuron: µm Dendrites animals have Cell body Axons of myo-epithelia Axon for contraction. neurons m 40 µ (Fluorescent LM) (Confocal LM) Heyer 4 Animal Tissues & Development Tissues è Organs è Organ Systems External environment Food CO2 Mouth O2 Animal body m Respiratory µ system Lung tissue (SEM) 250 Interstitial Heart fluid Nutrients Cells Circulatory system Digestive Excretory m system system m µ µ 50 Lining of small 100 Anus Blood vessels in kidney (SEM) intestine (SEM) Unabsorbed Metabolic waste matter (feces) products (nitrogenous waste) Body Symmetry • Developmental pattern formation results in Bauplan: symmetry of growth and regional specialization Radial symmetry. The parts Ger. “Life Plan” (pl: baupläne) of a radial animal, such as a sea anemone (phylum Cnidaria), radiate from the center. Any imaginary slice The arrangement, pattern, and through the central axis divides the animal into development of tissues, organs, and mirror images. systems unique to a particular type of Bilateral symmetry. A organism. bilateral animal, such as a lobster (phylum Arthropoda), has a left side and a right side. Only one imaginary cut divides the animal into mirror-image halves. Figure 32.7 (c) Variations in Acoelomate. flatworms Body covering Coelom (from ectoderm) Tissue- filled region (from Eucoelomate Gastrulation – Formation of coelom (body mesoderm) cavity) allows movement of • Coelom development in open vs. closed circulation organs within the body, Digestive tract esp. gut expansion & motility (from endoderm) (b) Pseudocoelomate. nematode worm Body covering • Acoelomate: no
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